# Borrow a lot from openai baselines:
# https://github.com/openai/baselines/blob/master/baselines/common/atari_wrappers.py

import warnings
from collections import deque

import cv2
import gymnasium as gym
import numpy as np

from tianshou.env import ShmemVectorEnv
from tianshou.highlevel.env import DiscreteEnvironments, EnvFactory
from tianshou.highlevel.trainer import TrainerStopCallback, TrainingContext

try:
    import envpool
except ImportError:
    envpool = None


def _parse_reset_result(reset_result):
    contains_info = (
        isinstance(reset_result, tuple)
        and len(reset_result) == 2
        and isinstance(reset_result[1], dict)
    )
    if contains_info:
        return reset_result[0], reset_result[1], contains_info
    return reset_result, {}, contains_info


class NoopResetEnv(gym.Wrapper):
    """Sample initial states by taking random number of no-ops on reset.

    No-op is assumed to be action 0.

    :param gym.Env env: the environment to wrap.
    :param int noop_max: the maximum value of no-ops to run.
    """

    def __init__(self, env, noop_max=30):
        super().__init__(env)
        self.noop_max = noop_max
        self.noop_action = 0
        assert env.unwrapped.get_action_meanings()[0] == "NOOP"

    def reset(self, **kwargs):
        _, info, return_info = _parse_reset_result(self.env.reset(**kwargs))
        if hasattr(self.unwrapped.np_random, "integers"):
            noops = self.unwrapped.np_random.integers(1, self.noop_max + 1)
        else:
            noops = self.unwrapped.np_random.randint(1, self.noop_max + 1)
        for _ in range(noops):
            step_result = self.env.step(self.noop_action)
            if len(step_result) == 4:
                obs, rew, done, info = step_result
            else:
                obs, rew, term, trunc, info = step_result
                done = term or trunc
            if done:
                obs, info, _ = _parse_reset_result(self.env.reset())
        if return_info:
            return obs, info
        return obs


class MaxAndSkipEnv(gym.Wrapper):
    """Return only every `skip`-th frame (frameskipping) using most recent raw observations (for max pooling across time steps).

    :param gym.Env env: the environment to wrap.
    :param int skip: number of `skip`-th frame.
    """

    def __init__(self, env, skip=4):
        super().__init__(env)
        self._skip = skip

    def step(self, action):
        """Step the environment with the given action.

        Repeat action, sum reward, and max over last observations.
        """
        obs_list, total_reward = [], 0.0
        new_step_api = False
        for _ in range(self._skip):
            step_result = self.env.step(action)
            if len(step_result) == 4:
                obs, reward, done, info = step_result
            else:
                obs, reward, term, trunc, info = step_result
                done = term or trunc
                new_step_api = True
            obs_list.append(obs)
            total_reward += reward
            if done:
                break
        max_frame = np.max(obs_list[-2:], axis=0)
        if new_step_api:
            return max_frame, total_reward, term, trunc, info

        return max_frame, total_reward, done, info


class EpisodicLifeEnv(gym.Wrapper):
    """Make end-of-life == end-of-episode, but only reset on true game over.

    It helps the value estimation.

    :param gym.Env env: the environment to wrap.
    """

    def __init__(self, env):
        super().__init__(env)
        self.lives = 0
        self.was_real_done = True
        self._return_info = False

    def step(self, action):
        step_result = self.env.step(action)
        if len(step_result) == 4:
            obs, reward, done, info = step_result
            new_step_api = False
        else:
            obs, reward, term, trunc, info = step_result
            done = term or trunc
            new_step_api = True

        self.was_real_done = done
        # check current lives, make loss of life terminal, then update lives to
        # handle bonus lives
        lives = self.env.unwrapped.ale.lives()
        if 0 < lives < self.lives:
            # for Qbert sometimes we stay in lives == 0 condition for a few
            # frames, so its important to keep lives > 0, so that we only reset
            # once the environment is actually done.
            done = True
            term = True
        self.lives = lives
        if new_step_api:
            return obs, reward, term, trunc, info
        return obs, reward, done, info

    def reset(self, **kwargs):
        """Calls the Gym environment reset, only when lives are exhausted.

        This way all states are still reachable even though lives are episodic, and
        the learner need not know about any of this behind-the-scenes.
        """
        if self.was_real_done:
            obs, info, self._return_info = _parse_reset_result(self.env.reset(**kwargs))
        else:
            # no-op step to advance from terminal/lost life state
            step_result = self.env.step(0)
            obs, info = step_result[0], step_result[-1]
        self.lives = self.env.unwrapped.ale.lives()
        if self._return_info:
            return obs, info
        return obs


class FireResetEnv(gym.Wrapper):
    """Take action on reset for environments that are fixed until firing.

    Related discussion: https://github.com/openai/baselines/issues/240.

    :param gym.Env env: the environment to wrap.
    """

    def __init__(self, env):
        super().__init__(env)
        assert env.unwrapped.get_action_meanings()[1] == "FIRE"
        assert len(env.unwrapped.get_action_meanings()) >= 3

    def reset(self, **kwargs):
        _, _, return_info = _parse_reset_result(self.env.reset(**kwargs))
        obs = self.env.step(1)[0]
        return (obs, {}) if return_info else obs


class WarpFrame(gym.ObservationWrapper):
    """Warp frames to 84x84 as done in the Nature paper and later work.

    :param gym.Env env: the environment to wrap.
    """

    def __init__(self, env):
        super().__init__(env)
        self.size = 84
        self.observation_space = gym.spaces.Box(
            low=np.min(env.observation_space.low),
            high=np.max(env.observation_space.high),
            shape=(self.size, self.size),
            dtype=env.observation_space.dtype,
        )

    def observation(self, frame):
        """Returns the current observation from a frame."""
        frame = cv2.cvtColor(frame, cv2.COLOR_RGB2GRAY)
        return cv2.resize(frame, (self.size, self.size), interpolation=cv2.INTER_AREA)


class ScaledFloatFrame(gym.ObservationWrapper):
    """Normalize observations to 0~1.

    :param gym.Env env: the environment to wrap.
    """

    def __init__(self, env):
        super().__init__(env)
        low = np.min(env.observation_space.low)
        high = np.max(env.observation_space.high)
        self.bias = low
        self.scale = high - low
        self.observation_space = gym.spaces.Box(
            low=0.0,
            high=1.0,
            shape=env.observation_space.shape,
            dtype=np.float32,
        )

    def observation(self, observation):
        return (observation - self.bias) / self.scale


class ClipRewardEnv(gym.RewardWrapper):
    """clips the reward to {+1, 0, -1} by its sign.

    :param gym.Env env: the environment to wrap.
    """

    def __init__(self, env):
        super().__init__(env)
        self.reward_range = (-1, 1)

    def reward(self, reward):
        """Bin reward to {+1, 0, -1} by its sign. Note: np.sign(0) == 0."""
        return np.sign(reward)


class FrameStack(gym.Wrapper):
    """Stack n_frames last frames.

    :param gym.Env env: the environment to wrap.
    :param int n_frames: the number of frames to stack.
    """

    def __init__(self, env, n_frames):
        super().__init__(env)
        self.n_frames = n_frames
        self.frames = deque([], maxlen=n_frames)
        shape = (n_frames, *env.observation_space.shape)
        self.observation_space = gym.spaces.Box(
            low=np.min(env.observation_space.low),
            high=np.max(env.observation_space.high),
            shape=shape,
            dtype=env.observation_space.dtype,
        )

    def reset(self, **kwargs):
        obs, info, return_info = _parse_reset_result(self.env.reset(**kwargs))
        for _ in range(self.n_frames):
            self.frames.append(obs)
        return (self._get_ob(), info) if return_info else self._get_ob()

    def step(self, action):
        step_result = self.env.step(action)
        if len(step_result) == 4:
            obs, reward, done, info = step_result
            new_step_api = False
        else:
            obs, reward, term, trunc, info = step_result
            new_step_api = True
        self.frames.append(obs)
        if new_step_api:
            return self._get_ob(), reward, term, trunc, info
        return self._get_ob(), reward, done, info

    def _get_ob(self):
        # the original wrapper use `LazyFrames` but since we use np buffer,
        # it has no effect
        return np.stack(self.frames, axis=0)


def wrap_deepmind(
    env_id,
    episode_life=True,
    clip_rewards=True,
    frame_stack=4,
    scale=False,
    warp_frame=True,
):
    """Configure environment for DeepMind-style Atari.

    The observation is channel-first: (c, h, w) instead of (h, w, c).

    :param str env_id: the atari environment id.
    :param bool episode_life: wrap the episode life wrapper.
    :param bool clip_rewards: wrap the reward clipping wrapper.
    :param int frame_stack: wrap the frame stacking wrapper.
    :param bool scale: wrap the scaling observation wrapper.
    :param bool warp_frame: wrap the grayscale + resize observation wrapper.
    :return: the wrapped atari environment.
    """
    assert "NoFrameskip" in env_id
    env = gym.make(env_id)
    env = NoopResetEnv(env, noop_max=30)
    env = MaxAndSkipEnv(env, skip=4)
    if episode_life:
        env = EpisodicLifeEnv(env)
    if "FIRE" in env.unwrapped.get_action_meanings():
        env = FireResetEnv(env)
    if warp_frame:
        env = WarpFrame(env)
    if scale:
        env = ScaledFloatFrame(env)
    if clip_rewards:
        env = ClipRewardEnv(env)
    if frame_stack:
        env = FrameStack(env, frame_stack)
    return env


def make_atari_env(task, seed, training_num, test_num, **kwargs):
    """Wrapper function for Atari env.

    If EnvPool is installed, it will automatically switch to EnvPool's Atari env.

    :return: a tuple of (single env, training envs, test envs).
    """
    if envpool is not None:
        if kwargs.get("scale", 0):
            warnings.warn(
                "EnvPool does not include ScaledFloatFrame wrapper, "
                "please set `x = x / 255.0` inside CNN network's forward function.",
            )
        # parameters convertion
        train_envs = env = envpool.make_gymnasium(
            task.replace("NoFrameskip-v4", "-v5"),
            num_envs=training_num,
            seed=seed,
            episodic_life=True,
            reward_clip=True,
            stack_num=kwargs.get("frame_stack", 4),
        )
        test_envs = envpool.make_gymnasium(
            task.replace("NoFrameskip-v4", "-v5"),
            num_envs=test_num,
            seed=seed,
            episodic_life=False,
            reward_clip=False,
            stack_num=kwargs.get("frame_stack", 4),
        )
    else:
        warnings.warn(
            "Recommend using envpool (pip install envpool) to run Atari games more efficiently.",
        )
        env = wrap_deepmind(task, **kwargs)
        train_envs = ShmemVectorEnv(
            [
                lambda: wrap_deepmind(task, episode_life=True, clip_rewards=True, **kwargs)
                for _ in range(training_num)
            ],
        )
        test_envs = ShmemVectorEnv(
            [
                lambda: wrap_deepmind(task, episode_life=False, clip_rewards=False, **kwargs)
                for _ in range(test_num)
            ],
        )
        env.seed(seed)
        train_envs.seed(seed)
        test_envs.seed(seed)
    return env, train_envs, test_envs


class AtariEnvFactory(EnvFactory):
    def __init__(self, task: str, seed: int, frame_stack: int, scale: int = 0):
        self.task = task
        self.seed = seed
        self.frame_stack = frame_stack
        self.scale = scale

    def create_envs(self, num_training_envs: int, num_test_envs: int) -> DiscreteEnvironments:
        env, train_envs, test_envs = make_atari_env(
            task=self.task,
            seed=self.seed,
            training_num=num_training_envs,
            test_num=num_test_envs,
            scale=self.scale,
            frame_stack=self.frame_stack,
        )
        return DiscreteEnvironments(env=env, train_envs=train_envs, test_envs=test_envs)


class AtariStopCallback(TrainerStopCallback):
    def __init__(self, task: str):
        self.task = task

    def should_stop(self, mean_rewards: float, context: TrainingContext) -> bool:
        env = context.envs.env
        if env.spec.reward_threshold:
            return mean_rewards >= env.spec.reward_threshold
        if "Pong" in self.task:
            return mean_rewards >= 20
        return False
